1. Field of the Invention
The present invention relates to a feed-control valve for attachment to an inlet or discharge port in a container or hopper for containing grain such as rice or wheat, particles such as pellets of plastics or tablets, or powdery material such as wheat or coffee powder.
2. Description of the Prior Art
Known valves for use in an inlet or discharge port in a container or hopper for containing granular powdery material include a mechanically operated valve body, which is liable to malfunction due to deposits or jamming of the grainy or powdery material. The prior valves are disadvantageous in that they are awkward to maintain and clean especially when to change the kind of a material to be conveyed. The valves are complex in structure because of a required degree of sealing against leakage, require a number of steps to assemble, and are expensive to construct.
There has been an attempt to develop a valve which has a flexible inner tube that can be contracted or squeezed radially inwardly in a direction to close a passage through the inner tube. However, a means for squeezing the inner tube has been unsatisfactory in that it fails to close the passage completely against leakage.